1. Field of the Invention
The present invention relates to a device for measuring the bonding load in a wire bonding machine.
2. Prior Art
In wire bonding machines, bonding wires are passed through capillaries which are attached to the tip of bonding arms and then pressed against the electrodes of semiconductor pellets and the leads of an outer lead frame so that bonding is performed between the electrodes and the leads in order to connect them. Thus, the bonding load with which the capillaries press the wires against the electrodes and leads have a great deal of effect on the quality of bonding. It is, therefore, necessary to measure and know the bonding load so that the bonding load is set as a predetermined appropriate value.
Conventionally, the measurement of the bonding load is performed using a tension gauge as shown in FIG. 6.
A wire 50 having a loop 50a at one end thereof is attached to the measuring lever 34 of the tension gauge 31. The loop 50a is hooked on the capillary fastening screw 7 which attaches the capillary 6 to the bonding arm 5, and then the tension gauge 31 held in hand is pulled upward. The bonding load is thus read from the scale of the tension gauge 31. If the read value is not equal to a set value, the bonding load is adjusted by increasing and decreasing the voltage of a linear motor which applies the bonding load to the bonding arm 5.
Thus, in the prior art, the bonding load is measured by a hand-held tension gauge 31. However, hands tend to be unstable when holding a gauge, and it is likely that measurement differs from person to person. Thus, the reliability of the measured value tends to be low. Furthermore, since the stable measurement value cannot be obtained easily, it takes a considerable period of time to adjust the bonding load to a set value.